Characterization and Modeling of Epitaxially Grown BST on a Conducting Oxide Electrode

This work presents a characterization technique and an EM-model for a thin film BST50 varactor grown on the oxide electrode material SMO, describing the benefits and limits of this characterization technique. Effective capacitance, Q factor, ESR and leakage current are evaluated and analyzed to understand the dominating mechanisms for the overall characteristic. The Q factor for this 13.3 pF varactor is 20.5 at 1 GHz. The extracted permittivity is 365, indicating a good BST crystal quality despite only 80 nm film thickness. The tunability at battery voltage level 3.7 V bias voltage (\pmb46 V/μm) is 67.8 %. The EM model shows very high Q factors up to 6 GHz, revealing outstandingly high potential for this oxide varactor with Q factors of up to 70 at 1 GHz, while still maintaining its large tunability. Hence, the ability to epitaxially grow BST on structurally similar SMO allows for very thin BST thicknesses with very low defect density, and thus, very high tunability at very low voltage below 3.7 volts.